Multilayer ceramic capacitor

ABSTRACT

A multilayer ceramic capacitor includes a laminated body including an inner layer portion including ceramic dielectric layers and internal electrodes, and outer layer portions including ceramic dielectric layers. External electrodes connected to the internal electrodes are provided on both ends of the laminated body. The main constituent of the inner layer portion is a perovskite-type compound represented by ABO 3 . The outer layer portions include first outer layers and second outer layers respectively containing oxides that differ from each other in main constituents, and boundary reaction layers are provided between the first outer layers and the second outer layers. First ceramic dielectric layers outside the boundary reaction layers differ in color from second ceramic dielectric layers inside the boundary reaction layers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multilayer ceramic capacitorincluding a dielectric ceramic.

2. Description of the Related Art

In general, a multilayer ceramic capacitor is composed of a laminatedbody in the form of a cuboid and external electrodes. The laminated bodyhas ceramic dielectric layers, and internal electrodes disposed to beopposed to each other between the ceramic dielectric layers and extendedto both ends of the laminated body. The external electrodes areconnected to the extended internal electrodes at both ends of thelaminated body. This laminated body includes an inner layer part andouter layer parts. The inner layer part has a plurality of internalelectrodes disposed to be opposed to each other. The outer layer partseach refer to a part between two internal electrodes disposed outermostamong the plurality of internal electrodes and side surfaces of thelaminated body opposed to the two internal electrodes, that is, a partof the laminated body outside the inner layer part. The outer layerparts and the inner layer part are typically formed from the samematerial (for example, see Japanese Patent Application Laid-Open No.6-084692).

In addition, in mounting the multilayer ceramic capacitor onto a circuitboard, depending on the orientation of the multilayer ceramic capacitor,the circuit board may be disposed parallel to the internal electrodes,or the circuit board may be disposed perpendicular to the internalelectrodes. The multilayer ceramic capacitor may, depending on such apositional relationship between the circuit board and the internalelectrodes, vary in floating capacitance value to influencecharacteristics of the multilayer ceramic capacitor.

Therefore, for mounting the multilayer ceramic capacitor onto a circuitboard, when the multilayer ceramic capacitor is packaged with theorientation of the internal electrodes aligned in advance so as to makeuniform the positional relationship between the circuit board and theinternal electrodes, the capacitor can be mounted so as to align thepositional relationship between the circuit board and the internalelectrodes, and variations in characteristics of the multilayer ceramiccapacitor can be reduced.

However, because the internal electrodes are buried in the laminatedbody, there has been a problem that it is difficult to recognize thelaminating direction of the internal electrodes by the appearance of themultilayer ceramic capacitor when the multilayer ceramic capacitor issquare or rectangular close to square in cross section.

SUMMARY OF THE INVENTION

Therefore, preferred embodiments of the present invention provide amultilayer ceramic capacitor which is able to indicate a mountingorientation in a case of mounting the multilayer ceramic capacitor ontoa board or substrate.

A multilayer ceramic capacitor according to a preferred embodiment ofthe present invention includes a laminated body including an inner layerportion that includes a plurality of ceramic dielectric layerslaminated, with internal electrodes provided on the plurality of ceramicdielectric layers, and an outer layer portion that includes a pluralityof ceramic dielectric layers laminated outside the inner layer portion,with no internal electrodes provided on the plurality of ceramicdielectric layers; and external electrodes provided on both ends of thelaminated body, wherein the inner layer portion contains, as its mainconstituent, a perovskite-type compound represented by ABO₃ (where Arepresents one or more of Ba, Sr, and Ca, B represents one or more ofTi, Zr, and Hf, and O represents oxygen), the outer layer portionincludes at least: as an outermost layer, a first outer layer containingan oxide as its main constituent, and a second outer layer containing,as its main constituent, an oxide that is different from the oxide ofthe first outer layer, a boundary reaction layer is disposed between thefirst outer layer and the second outer layer, and further, the boundaryreaction layer contains at least one element other than oxygen amongelements constituting the oxide in the first outer layer adjacent to theboundary reaction layer, and at least one element other than oxygenamong elements constituting the oxide in the second outer layer adjacentto the boundary reaction layer, and a surface of the first outer layerdiffers in color from a surface of the inner layer portion.

In addition, in a multilayer ceramic capacitor according to a preferredembodiment of the present invention, the oxide in the second outer layeris preferably a perovskite-type compound.

Furthermore, in a multilayer ceramic capacitor according to a preferredembodiment of the present invention, the oxide in the first outer layeris preferably a perovskite-type compound.

In a multilayer ceramic capacitor according to a preferred embodiment ofthe present invention, the first outer layer of the laminated bodydiffers in surface color from the inner layer portion. Therefore, thelaminating direction of the internal electrodes is able to be confirmedfrom the appearance of the multilayer ceramic capacitor, and themultilayer ceramic capacitor is able to be mounted in consideration ofthe positional relationship between a board and the internal electrodesof the multilayer ceramic capacitor.

In addition, in a multilayer ceramic capacitor according to a preferredembodiment of the present invention, characteristics of the multilayerceramic capacitor are improved when the oxide in the second outer layeror in the first outer layer is a perovskite-type compound.

According to a preferred embodiment of the present invention, the planarorientation of the internal electrodes is able to be reliably determinedby virtue of the difference in color at side surfaces of the laminatedbody of the multilayer ceramic capacitor. Therefore, in the case ofmounting the multilayer ceramic capacitor onto a board, substrate or thelike, the multilayer ceramic capacitor is able to be mounted on theboard or substrate in consideration of the positional relationshipbetween the board or substrate and the internal electrodes in thelaminated body.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external perspective view illustrating a multilayer ceramiccapacitor according to a preferred embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating the internal structure ofthe multilayer ceramic capacitor shown in FIG. 1.

FIG. 3 is a cross-sectional view illustrating another example of theinternal structure of the multilayer ceramic capacitor shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is an external perspective view illustrating a multilayer ceramiccapacitor according to a preferred embodiment of the present invention.FIG. 2 is a cross-sectional view illustrating the internal structure ofthe multilayer ceramic capacitor shown in FIG. 1.

The multilayer ceramic capacitor 10 includes a laminated body 12 in theform of, for example, a cuboid. The laminated body 12 includes ceramicdielectric layers and internal electrodes laminated alternately, and maybe square or rectangular in cross-sectional shape including the widthdirection and the height direction. The ceramic dielectric layersconstituting the laminated body 12 preferably have a thickness on theorder of about 0.5 μm to about 5 μm, and the total number of layerslaminated is 100 to 600, for example.

The laminated body 12 includes an inner layer portion 14 and outer layerportions 16 as shown in FIG. 2.

The inner layer portion 14 includes a plurality of ceramic dielectriclayers 18 and internal electrodes 20 alternately laminated. The adjacentinternal electrodes 20 are opposed to each other with the ceramicdielectric layer 18 interposed therebetween. Further, the plurality ofinternal electrodes 20 is extended alternately to two end surfaces ofthe laminated body 12 opposed to each other. More specifically, theadjacent internal electrodes 20 are respectively extended to thedifferent end surfaces of the laminated body 12. The internal electrodes20 are preferably formed from, for example, Ni or Cu, and laminated tohave on the order of 80 to 500 sheets of electrodes, for example. Theinner layer portion 14 defines a portion of the laminated body 12, andrefers to the range between the two internal electrodes 20 at both endsamong the internal electrodes 20 laminated.

The outer layer portions 16 include a plurality of ceramic dielectriclayers 22 with no internal electrode 20 provided therein, and disposedso as to sandwich both sides of the inner layer portion 14. Boundaryreaction layers 24 are provided midway in the outer layer portions 16.More specifically, first outer layers 22 a are disposed outside theboundary reaction layers 24, whereas second outer layers 22 b aredisposed inside the boundary reaction layers 24. More specifically, thefirst outer layers 22 a define outermost layers.

It is to be noted that the first outer layers 22 a and the second outerlayers 22 b may each correspond to one sheet of ceramic dielectriclayer, or a plurality of ceramic dielectric layers.

Further, the respective outer layer portions 16 that sandwich the bothsides of the inner layer portion 14 may differ in thickness. Further,still other outer layers may be disposed between the second outer layers22 b and the inner layer portion 14.

It is to be noted that first ceramic dielectric layers 26 are differentin color from second ceramic dielectric layers 28 and are preferablywhite in color. In this regard, the first ceramic dielectric layers 26correspond with the first outer layers 22 a of the outer layer portions16, which is disposed outside the boundary reaction layers 24. Inaddition, the second ceramic dielectric layers 28 include the ceramicdielectric layers 18 of the inner layer portion 14, and the second outerlayers 22 b of the outer layer portions 16, which are disposed insidethe boundary reaction layers 24. It is to be noted that the boundaryreaction layers 24 may be provided between the inner layer portion 14and the outer layer portions 16. In this case, the ceramic dielectriclayers 22 constituting the outer layer portions 16 all correspond to thefirst ceramic dielectric layers 26, whereas the ceramic dielectriclayers 18 constituting the inner layer portion 14 all correspond to thesecond ceramic dielectric layers 28. Thus, the inner layer portion 14and the outer layer portions 16 are able to be strongly coupled. Inaddition, the side surfaces of the laminated body 12 at ends in thelaminating direction (side surfaces including the width direction andlength direction in FIG. 1) is able to be distinguished from the sidesurfaces with ends of the second ceramic dielectric layers 28 exposed(side surfaces including the height direction and length direction inFIG. 1). More specifically, the side surface of the laminated body 12 atthe both ends in the laminating direction is able to be distinguished bythe color of the first ceramic dielectric layers 26.

The main constituent of the ceramic dielectric layers constituting thesecond ceramic dielectric layers 28 is a perovskite-type compoundrepresented by ABO₃. In this regard, A contains one or more of Ba, Sr,and Ca, B contains one or more of Ti, Zr, and Hf, and O representsoxygen. Furthermore, the ceramic dielectric layers 18 constituting theinner layer portion 14 contains Dy, Mn, Mg, and Si as additivematerials.

Having the composition as mentioned above is able to be confirmed whenafter removing the first ceramic dielectric layers 26 with sand paper orthe like, the second ceramic dielectric layers 28 left are made into apowder, dissolved in an acid, and subjected to ICP emissionspectrometry.

In addition, the main constituent of the first outer layers 22 aconstituting the first ceramic dielectric layers 26 includes an oxidecontaining Ca and Zr, and Si and Mn as additive materials. In addition,the main constituent of the second outer layers 22 b constituting thesecond ceramic dielectric layers 28 includes an oxide containing Ba andTi, and Si as an additive material. In addition, the oxide which is themain constituent of the first outer layer 22 a and second outer layer 22b is preferably perovskite-type compound.

In addition, the boundary reaction layers 24 between the first outerlayers 22 a and the second outer layers 22 b contain at least oneelement other than oxygen among the elements constituting the oxide inthe first outer layers 22 a, and at least one element other than oxygenamong the elements constituting the oxide in the second outer layers 22b.

Having the compositions as mentioned above is able to be confirmed whenthe first outer layers 22 a and the second outer layers 22 b includingthese main constituents are made into powders, dissolved in an acid, andsubjected to ICP emission spectrometry.

Having the compositions as mentioned above is able to be also confirmedin such a way that the laminated body 12 is wrapped with a resin, andthen polished to expose a cross section of the first outer layers 22 a,second outer layers 22 b, and boundary reaction layers 24 cut in thethickness direction, and the cross section is subjected to compositionanalysis by WDX.

It is to be noted that one or more elements other than oxygen, whichconstitute the main constituent of the second outer layers 22 b, maydiffuse across the boundary reaction layers 24 into the first outerlayers 22 a.

Further, around the boundaries between the second outer layers 22 b andthe boundary reaction layers 24 in the second outer layers 22 b, theelements constituting the main constituent of the second outer layers 22b define the boundary reaction layers 24, and additionally, diffusetoward the first outer layers 22 a as described above, so that portionsin which the element concentration is made lower than the averageconcentration in the second outer layers 22 b are formed.

External electrodes 30 extend along both ends in the longer direction ofthe laminated body 12 so as to be connected to the internal electrodes20. The external electrodes 30 wrap around the four side surfaces fromthe end surfaces of the laminated body 12. For the external electrodes30, underlying metal layers are formed preferably by immersing ends ofthe laminated body 12 in an electrode paste, and carrying out sintering.Ni plating and Sn plating are applied onto underlying metal layers toform the external electrodes 30.

In the multilayer ceramic capacitor 10 shown in FIG. 2, due to the factthat the color of the first outer layers 22 a in the outer layer portion16 of the laminated body 12 differs from the color of the inner layerportion 14, the laminating direction of the internal electrodes 20 isable to be confirmed from the appearance of the multilayer ceramiccapacitor by virtue of the difference in color, and the multilayerceramic capacitor 10 is able to be mounted in consideration of thepositional relationship between a board or substrate and the internalelectrodes 20 of the multilayer ceramic capacitor.

In addition, in the multilayer ceramic capacitor 10 shown in FIG. 2,while the oxides as the main constituents contained in the first outerlayers 22 a and the second outer layers 22 b differ in the outer layerportions 16 of the laminated body 12, the first outer layers 22 a andthe second outer layers 22 b are able to be strongly coupled because theboundary reaction layers 24 are provided at the boundary surfacesbetween the first outer layers 22 a and the second outer layers 22 b. Inthis regard, the fact that the oxides differ means that, except forminute amounts of elements like impurities, the constituent elements ofthe oxide in the first outer layers 22 a include at least one or moreelements that differ from the constituent elements of the oxide in thesecond outer layers 22 b, or that the constituent elements of the oxidein the second outer layers 22 b include at least one or more elementsthat differ from the constituent elements of the oxide in the firstouter layers 22 a.

It is to be noted that when the oxide as the main constituent of thesecond outer layers 22 b and the perovskite-type compound as the mainconstituent of the ceramic dielectric layers 18 constituting the innerlayer portion 14 are compounds of the same sort, the second outer layers22 b and the inner layer portion 14 is able to be strongly coupled.

In this regard, the same sort refers to compounds that have the sameconstituent elements and crystal structure, except for minute amounts ofelements like impurities, and the constituent element ratios may bedifferent.

Furthermore, another preferred embodiment of the multilayer ceramiccapacitor according to a preferred embodiment of the present inventionwill be described. FIG. 3 is a cross-sectional view illustrating anotherpreferred embodiment of the internal structure of the multilayer ceramiccapacitor 10′ according to a preferred embodiment of the presentinvention. The multilayer ceramic capacitor 10′ includes a first outerlayer 22 a and a second outer layer 22 b provided only on one side of aninner layer portion 14, unlike the multilayer ceramic capacitor 10. Onthe other side of the inner layer portion 14, the same ceramicdielectric layers as ceramic dielectric layers 18 of the inner layerportion 14 are laminated to provide an outer layer portion 16.

The multilayer ceramic capacitor 10′ shown in FIG. 3 herein produces asimilar effect to the above-described multilayer ceramic capacitor 10shown in FIG. 2.

It is to be noted that the boundary reaction layers 24 are preferablydrawn as continuous sheets of layers in FIGS. 2 and 3, but may bediscontinuous layers.

Next, a non-limiting example of a method for manufacturing a multilayerceramic capacitor will be described for manufacturing the multilayerceramic capacitor 10 shown in FIG. 1.

In order to prepare the multilayer ceramic capacitor 10, BaTiO₃ isprepared which is a ceramic raw material powder for forming the innerlayer portion 14.

For example, first, a BaCO₃ powder and a TiO₂ powder are weighed so thatthe ratio of Ba/Ti is 1.001, and subjected to wet mixing with a millthat uses ZrO₂ balls. This mixed slurry is dried, and then heated to1000° C. to provide a BaTiO₃ powder of 0.16 μm in average particle size.Then, to 100 parts by mol of the BaTiO₃ powder, 1.0 part by mol of Dy,1.2 parts by mol of Mg, 0.2 part by mol of Mn, and 1.0 part by mol of Baare each added as a metal soap solution, and 1.5 parts by mol of Si isfurther added as an alkoxide. Subsequently, the mixture is subjected towet mixing with a mill that uses ZrO₂ balls in a mixing system oftoluene and ethyl alcohol as a dispersion medium. After the removal ofthe dispersion medium, the mixture is subjected to heat treatment at500° C. to remove the organic component, and subjected to particle sizeregulation to provide a ceramic raw material powder for forming theinner layer portion 14. This ceramic raw material powder for forming theinner layer portion 14 is, with the addition of a polybutyral-basedbinder and a plasticizer thereto, and then with the addition of a mixeddispersion medium of toluene and ethyl alcohol thereto, subjected to wetmixing with a mill that uses ZrO₂ balls, thus providing slurry. Next,this slurry is formed with a gravure coater into ceramic green sheets of1.0 μm in thickness to prepare ceramic green sheets for forming theinner layer portion 14.

Likewise, a ceramic raw material powder for forming the first outerlayers 22 a and a ceramic raw material powder for forming the secondouter layers 22 b are also each formed into ceramic green sheets toprepare ceramic green sheets for forming the first outer layers 22 a andceramic green sheets for forming the second outer layers 22 b.

The ceramic raw material powder for forming the second outer layer 22 bis the same as the ceramic raw material powder for forming the innerlayer portion 14.

On the other hand, the ceramic raw material powder for forming the firstouter layers 22 a is prepared as follows.

For example, first, a CaCO₃ powder and a ZrO₂ powder are weighed so thatthe ratio of Zr/Ti is 1.000, and subjected to wet mixing with a millthat uses ZrO₂ balls. This mixed slurry is dried, and then heated to1100° C. to provide a CaZrO₃ powder of 0.25 μm in average particle size.Then, to 100 parts by mol of the CaZrO₃ powder, 1.0 part by mol of MnCO₃and 1.5 parts by mol of SiO₂ are each added as a powder. Subsequently,the mixture is mixed with a mill that uses ZrO₂ balls in pure water as adispersion medium. The mixture is dried, and then subjected to particlesize regulation to provide a ceramic raw material powder for forming thefirst outer layers 22 a.

Subsequently, onto the ceramic green sheets formed from the ceramic rawmaterial powder for forming the inner layer portion 14, a conductivepaste (for example, Ni paste) prepared separately is applied by screenprinting, thus forming conductive film patterns to define and functionas internal electrodes. The conductive film patterns are formed by, forexample, screen printing or gravure printing. The multiple ceramic greensheets with the conductive film patterns formed are laminated so as toalternate the sides to which the conductive film patterns are extended,thus providing a portion corresponding to the inner layer portion 14.

Next, the ceramic green sheets with no conductive film patterns formedfor forming the second outer layers 22 b are laminated so as to sandwichthe inner layer portion 14. Then, furthermore, the ceramic green sheetsfor forming the first outer layers 22 a are laminated outside of theceramic green sheets for forming the second outer layers 22 b to formportions corresponding to the outer layer portions 16. In this way, amother laminated body is prepared.

It is to be noted that the ceramic green sheets for forming the firstouter layers 22 a to define and function as the first ceramic dielectriclayers 26 after firing and the ceramic green sheets for forming thefirst outer layers 22 b and ceramic dielectric layers 18 to define andfunction as the second ceramic dielectric layers 28 are preferablyformed in a way that such dielectric materials that differ in colorafter firing are selected as respectively described above. For example,a perovskite-type compound where the A-site element and the B-siteelement respectively have stable valences of +2 and +4, such as CaZrO₃,is used for the first ceramic dielectric layers 26, whereas aperovskite-type compound where the A-site element has a stable valenceof +2, while the B-site element has a valence varied depending on thefiring atmosphere, such as BaTiO₃, is used for the second ceramicdielectric layers 28. CaZrO₃ provides white ceramics, even in the caseof containing minute amounts of elements, such as Mn, that have valenceseasily varied depending on the firing atmosphere. BaTiO₃ has a colorthat is able to be controlled by adjusting the additive amounts ofelements, such as Mn, that have valences easily varied depending on thefiring atmosphere.

In addition, because calcium zirconate is higher in Young's modulus thanbarium titanate, the use of high dielectric constant BaTiO₃ for theinner layer portion 14 and of CaZrO₃ or the like for the outer layerportions 16 prevents the multilayer ceramic capacitor from vibrating dueto the electrostrictive effect of the dielectric ceramics. Therefore,the vibration of a circuit board due to the electrostrictive effect,sound-generating phenomenon referred to as so-called acoustic noise,which is caused when the multilayer ceramic capacitor is mounted on thecircuit board, is significantly reduced or prevented.

Next, this mother laminated body was cut into green laminated chips soas to have a desired size. Then, these green laminated bodies weresubjected to heat treatment at 270° C. in a N₂ atmosphere to burn andremove the binder. Thereafter, the green laminated chips with the binderburned and removed therefrom is subjected to firing for holding time of5 minutes at 1220° C. while the rate of temperature increase is 30°C./min at 800° C. or higher in a reducing atmosphere composed of aN₂—H₂-H₂O gas, thus providing the laminated body 12 where the boundaryreaction layers 24 are formed which contain at least one element otherthan oxygen among the elements constituting the oxide as the mainconstituent of the first outer layers 22 a and contain at least oneelement other than oxygen among the elements constituting the oxide asthe main constituent of the second outer layers 22 b. Further, barrelpolishing may be carried out before or after the firing, in order toround corners of the green laminated chips or the laminated body 12.

Furthermore, a conductive paste containing Cu as its main constituent isapplied to the both end surface parts of the laminated body 12 to whichthe conductive film patterns to define and function as the internalelectrodes 20 are extended, and baked at a predetermined temperature toform underlying electrodes. These underlying electrodes are subjected tonickel plating and tin plating by, for example, wet plating, thusforming the external electrodes 30. In this way, the desired multilayerceramic capacitor 10 is obtained.

EXPERIMENTAL EXAMPLE

In an experimental example, the following multilayer ceramic capacitorsaccording to Examples 1 to 4 and Comparative Examples 1 to 3 weremanufactured to evaluate the multilayer ceramic capacitors for bendingstrength and outer layer discrimination.

Example 1

1. Preparation of Ceramic Raw Material Powder for Forming Inner LayerPortion

The ceramic raw material powder for forming the inner layer portion 14was prepared by the method described below. A BaCO₃ powder and a TiO₂powder were weighed so that the ratio of Ba/Ti was 1.001, and subjectedto wet mixing with a mill using ZrO₂ balls. This mixed slurry was dried,and then heated to 1000° C. to provide a BaTiO₃ powder of 0.16 μm inaverage particle size. Then, to 100 parts by mol of the BaTiO₃ powder,1.0 part by mol of Dy, 1.2 parts by mol of Mg, 0.2 part by mol of Mn,and 1.0 part by mol of Ba were each added as a metal soap solution, and1.5 parts by mol of Si was further added as an alkoxide. Subsequently,the mixture was subjected to wet mixing with a mill using ZrO₂ balls ina mixing system of toluene and ethyl alcohol as a dispersion medium.After the removal of the dispersion medium, the mixture was subjected toheat treatment at 500° C. to remove the organic component, and subjectedto particle size regulation to prepare a ceramic raw material powder forforming the inner layer portion 14.

2. Preparation of Ceramic Raw Material Powder for Forming Outer LayerPortion

The ceramic raw material powder for forming the second outer layer 22 bin the outer layer portions 16 was made from the same materials as thematerials used in preparing the ceramic raw material powder for formingthe inner layer portion 14. Therefore, the main constituent of theceramic raw material powder for forming the second outer layers 22 b isBaTiO₃.

On the other hand, the ceramic raw material powder for forming the firstouter layers 22 a was prepared as follows. First, a CaCO₃ powder and aZrO₂ powder were weighed so that the ratio of Zr/Ti was 1.000, andsubjected to wet mixing with a mill using ZrO₂ balls.

This mixed slurry was dried, and then heated to 1100° C. to provide aCaZrO₃ powder of 0.25 μm in average particle size. To 100 parts by molof the CaZrO₃ powder, 1.0 part by mol of MnCO₃ and 1.5 parts by mol ofSiO₂ were each added as a powder, and the mixture was subjected to wetmixing with a mill using ZrO₂ balls in pure water as a dispersionmedium. The mixture was dried, and then subjected to particle sizeregulation to prepare a ceramic raw material powder for forming thefirst outer layers 22 a.

3. Preparation of Multilayer Ceramic Capacitor

The ceramic raw material powder for forming the inner layer portion 14was, with the addition of a polybutyral-based binder and a plasticizerthereto, and with the addition of toluene and ethyl alcohol thereto,subjected to wet mixing with a mill using ZrO₂ balls, thus providingslurry. Next, this slurry was formed with a gravure coater into ceramicgreen sheets of 1.0 μm in thickness. Likewise, the ceramic raw materialpowder for forming the first outer layers 22 a and the ceramic rawmaterial powder for forming the second outer layers 22 b were alsoformed into ceramic green sheets.

Onto the ceramic green sheets formed from the ceramic raw materialpowder for forming the inner layer portion 14, a Ni-containingconductive paste prepared separately was applied by screen printing,thus forming conductive film patterns to define and function as internalelectrodes 14. Thereafter, 400 of the sheets were laminated so as toalternate the sides to which the conductive film patterns were extended,thus providing the inner layer portion 14.

Subsequently, a mother laminated body was prepared by laminating 48 μmof the ceramic green sheets formed from the ceramic raw material powderfor forming the second outer layers 22 b so as to sandwich the innerlayer portion 14, and further laminating, on both outer sides of thelaminate, 7 μm of the ceramic green sheets formed from the ceramic rawmaterial powder for forming the first outer layers 22 a. This motherlaminated body was cut into green laminated chips so as to have adesired size.

The thus prepared green laminated chips were subjected to heat treatmentat 270° C. in a N₂ atmosphere to burn and remove the binder. Thereafter,the chips were subjected to firing for holding time of 5 minutes at1220° C. while the rate of temperature increase was 30° C./min at 800°C. or higher in a reducing atmosphere composed of a N₂—H₂—H₂O gas. Thelaminated body 12 obtained was 1.2 mm in length, 0.7 mm in width, and0.7 mm in height in terms of size, and prismatic in terms of shape whilebeing square in cross section. A conductive film paste containing Cu asits main constituent was applied to both end surface portions of thelaminated body 12 obtained, with the extended conductive film patternsto define and function as the internal electrodes 20, and baked at 800°C. to form underlying electrodes. Furthermore, surface layers of theunderlying electrodes were subjected to nickel plating and tin platingby wet plating to form the external electrodes 30. Then, a multilayerceramic capacitor was obtained as shown in FIG. 2.

It is to be noted that the element portion of the multilayer ceramiccapacitor obtained in this way was 0.85 μm in thickness.

Example 2

In Example 2, after the inner layer portion 14 was obtained in the sameway as in Example 1, on only one side thereof, the ceramic green sheetsformed from the ceramic raw material powder for forming the second outerlayers 22 b were laminated to reach 48 μm, and further on the surface ofthe sheets, the ceramic green sheets formed from the ceramic rawmaterial powder for forming the first outer layers 22 a were laminatedto reach 7 μm. On the other hand, on the other side of the inner layerportion 14, the ceramic green sheets formed from the ceramic rawmaterial powder for forming the inner layer portion 14 were laminated toreach 55 μm, thus preparing a mother laminated body. Thereafter, amultilayer ceramic capacitor according to Example 2 as shown in FIG. 3was obtained by cutting the mother laminated body into green laminatedchips, firing the chips, and forming the external electrodes 30 in thesame way as in Example 1.

Example 3

In Example 3, the oxide as the main constituent of the first outerlayers 22 a was SrZrO₃, unlike Example 1. In order to prepare ceramicgreen sheets formed from a ceramic raw material powder for forming thefirst outer layers 22 a, first, a SrCO₃ powder and a ZrO₂ powder wereweighed so that the ratio of Sr/Zr was 1.000, mixed and ground with amill using ZrO₂ balls, and then heated to 1050° C. to provide a SrZrO₃powder. To 100 parts by mol of the SrZrO₃ powder, 1.0 part by mol ofMgCO₃ and 2.5 parts by mol of SiO₂ were each added as a powder, and themixture was subjected to wet mixing with a mill using ZrO₂ balls in purewater as a dispersion medium. The mixture was dried, and then subjectedto particle size regulation to prepare a ceramic raw material powder forforming the first outer layers 22 a for use in Example 3.

Then, after the inner layer portion 14 was obtained in the same way asin Example 1, a mother laminated body was prepared by laminating 48 μmof the ceramic green sheets formed from the ceramic raw material powderfor forming the second outer layers 22 b so as to sandwich the innerlayer portion 14, and further laminating, on the surface of thelaminate, 7 μm of the ceramic green sheets formed from the ceramic rawmaterial powder for forming the first outer layers 22 a. Thereafter, amultilayer ceramic capacitor according to Example 3 was obtained bycutting the mother laminated body into green laminated chips, firing thechips, and forming the external electrodes 30 in the same way as inExample 1.

Example 4

In Example 4, the oxide as the main constituent of the first outerlayers 22 a was (Ba_(0.2)Sr_(0.8))TiO₃, unlike Example 1. In order toprepare ceramic green sheets formed from a ceramic raw material powderfor forming the first outer layers 22 a, first, a SrCO₃ powder, a BaCO₃powder, and a TiO₂ powder were mixed and ground, and then heated to1050° C. to provide a (Ba_(0.2)Sr_(0.8))TiO₃ powder. To 100 parts by molof the (Ba_(0.2)Sr_(0.8))TiO₃ powder, 2.0 parts by mol of MgCO₃, 1.5parts by mol of SiO₂, and 0.5 part by mol of Li₂O were each added as apowder, and the mixture was subjected to wet mixing with a mill usingZrO₂ balls in pure water as a dispersion medium. The mixture was dried,and then subjected to particle size regulation to prepare a ceramic rawmaterial powder for forming the first outer layers 22 a for use inExample 4.

Then, after the inner layer portion 14 was obtained in the same way asin Example 1, a mother laminated body was prepared by laminating 48 μmof the ceramic green sheets formed from the ceramic raw material powderfor forming the second outer layers 22 b so as to sandwich the innerlayer portion 14, and further laminating, on the surface of thelaminate, 7 μm of the ceramic green sheets formed from the ceramic rawmaterial powder for forming the first outer layers 22 a. Thereafter, amultilayer ceramic capacitor according to Example 4 was obtained bycutting the mother laminated body into green laminated chips, firing thechips, and forming the external electrodes 30 in the same way as inExample 1.

Comparative Example 1

In Comparative Example 1, BaTiO₃ of the same as the ceramic raw materialpowder for forming the inner layer portion 14 was used as the ceramicraw material powder for forming the outer layer portions 16, unlikeExample 1. Then, a multilayer ceramic capacitor according to ComparativeExample 1 was obtained by cutting the mother laminated body into greenlaminated chips, firing the chips, and forming the external electrodes30 to prepare a multilayer ceramic capacitor in the same way as inExample 1.

Comparative Example 2

In Comparative Example 2, the oxide as the main constituent of the firstouter layers 22 a was Ba(Ti_(0.05)Zr_(0.95))O₃, unlike Example 1. Inorder to prepare ceramic green sheets formed from a ceramic raw materialpowder for forming the first outer layers 22 a, first, a BaCO₃ powder, aTiO₂, and a ZrO₂ powder were mixed and ground, and then heated to 1050°C. to provide a Ba(Ti_(0.05)Zr_(0.95))O₃ powder. To 100 parts by mol ofthe Ba(Ti_(0.05)Zr_(0.95))O₃ powder, 0.25 part by mol of MnCO₃ and 1.5parts by mol of SiO₂ were each added as a powder, and the mixture wassubjected to wet mixing with a mill using ZrO₂ balls in pure water as adispersion medium. The mixture was dried, and then subjected to particlesize regulation to prepare a ceramic raw material powder for forming thefirst outer layers 22 a for use in Comparative Example 2.

Then, after the inner layer portion 14 was obtained in the same way asin Example 1, a mother laminated body was prepared by laminating 48 μmof the ceramic green sheets formed from the ceramic raw material powderfor forming the second outer layers 22 b so as to sandwich the innerlayer portion 14, and further laminating, on the surface of thelaminate, 7 μm of the ceramic green sheets formed from the ceramic rawmaterial powder for forming the first outer layers 22 a. Thereafter, amultilayer ceramic capacitor according to Comparative Example 2 wasobtained by cutting the mother laminated body into green laminatedchips, firing the chips, and forming the external electrodes 30 in thesame way as in Example 1.

Comparative Example 3

In Comparative Example 3, the oxide as the main constituent of the firstouter layers 22 a was CaZrO₃ like Example 1, while the additive for usein preparing the oxide differs in composition. To 100 parts by mol ofthe CaZrO₃ powder, 5.0 parts by mol of MnCO₃ and 2.0 parts by mol ofSiO₂ were each added as a powder, and the mixture was subjected to wetmixing with a mill using ZrO₂ balls in pure water as a dispersionmedium. The mixture was dried, and then subjected to particle sizeregulation to prepare a ceramic raw material powder for forming thefirst outer layers 22 a for use in Comparative Example 3.

Then, after the inner layer portion 14 was obtained in the same way asin Example 1, a mother laminated body was prepared by laminating 48 μmof the ceramic green sheets formed from the ceramic raw material powderfor forming the second outer layers 22 b so as to sandwich the innerlayer portion 14, and further laminating, on the surface of thelaminate, 7 μm of the ceramic green sheets formed from the ceramic rawmaterial powder for forming the first outer layers 22 a. Thereafter, amultilayer ceramic capacitor according to Comparative Example 3 wasobtained by cutting the mother laminated body into green laminatedchips, firing the chips, and forming the external electrodes 30 in thesame way as in Example 1.

4. Characterization in Example and Comparative Example

The respective multilayer ceramic capacitors according to the examplesand the comparative examples were subjected to the followingcharacterization.

Whether Boundary Reaction Layer is Formed or not

Cross sections (cross sections LT) of the multilayer ceramic capacitors10 according to the respective examples and the respective comparativeexamples in the height direction (direction T) and length direction(direction L) in FIG. 1 were exposed by polishing with the capacitorswrapped with a resin, the general outer layer portions were observedthrough reflection electron images under a scanning electron microscope(SEM), and element analyses were conducted by wavelength-dispersiveX-ray spectroscopy (WDX) to confirm whether boundary reaction layerswere formed or not. It is to be noted that the polishing was carried outto a depth on the order of ½ in the width direction.

Discrimination Between Color of Surface of First Outer Layer and Colorof Surface of Inner Layer Portion

The colors of the surfaces of the first outer layers 22 a werediscriminated visually from the color of the surface of the inner layerportion 14.

Bending Strength Test

Furthermore, central portions of the multilayer ceramic capacitors inthe length direction were subjected to a bending test in conformity withthe JIS standards (JISR1601) to conduct the evaluation of mechanicalstrength. The number of measurement samples was 20 for each of theexamples and for each of the comparative examples, and the results werecalculated as average values for the 20 samples. The determination wasmade on the basis of 25≦P (N/mm²) in terms of average bending strengthP, from the structures of the multilayer ceramic capacitors prepared inthe respective examples and the respective comparative examples. Whenthe average bending strength P meets 25≦P (N/mm²), the result is shownas “∘”, or if not, shown as “x”. The results are shown in Table 1.

TABLE 1 Bending Main Constituent of Ceramic Boundary Reaction Strengthof Outer layer portion Layer Test Second Outer First Outer FormedDetected Outer Layer 25 N/mm² Layer Layer or Not Element Discriminationor more Example 1 BaTiO₃ CaZrO₃ Yes Ba, Ca Possible ∘ Example 2 BaTiO₃CaZrO₃ Yes Ba, Ca Possible ∘ Example 3 BaTiO₃ SrZrO₃ Yes Ba, Sr Possible∘ Example 4 BaTiO₃ (Ba_(0.2)Sr_(0.8))TiO₃ Yes Ba, Sr, Ti Possible ∘ *Comparative Same Main Constituent in Outer No — Impossible ∘ Example 1layer portion and Inner Layer * Comparative BaTiO₃Ba(Ti_(0.05)Zr_(0.95))O₃ No — Impossible x Example 2 * ComparativeBaTiO₃ CaZrO₃ Yes Ba, Ca Impossible ∘ Example 3 * Outside of the scopeof the present invention

Table 1 shows the presence or absence of the boundary reaction layers24, availability of outer layer discrimination, and the results of thebending strength test, for each case of using the main constituent ofthe ceramic raw material powder for forming the first outer layers 22 aand the main constituent of the ceramic raw material powder for formingthe second outer layers 22 b in the respective examples and therespective comparative examples.

In Examples 1 through 4, it has been successfully confirmed from thereflection electron images that the boundary reaction layers 24 areformed in the outer layer portions 16. In addition, it has beensuccessfully confirmed from the wavelength-dispersive X-ray spectroscopythat the boundary reaction layers 24 contain at least one element otherthan oxygen among the elements constituting the main constituent of thefirst outer layers 22 a, and at least one element other than oxygenamong the elements constituting the main constituent of the second outerlayers 22 b. In this spectroscopy, when an element was detected as 0.1wt % or more, the element was considered to be contained. Morespecifically, 0.1 wt % or more of Ba and Ca were detected from theboundary reaction layers 24 in Examples 1 and 2, 0.1 wt % or more of Baand Sr were detected in Example 3, and 0.1 wt % or more of Ba, Sr, andTi were detected in Example 4. In addition, the surfaces of the firstouter layers 22 a were white in Examples 1 through 3, and somewhatdusky-white in Example 4. Thus, it has been possible to discriminate thesurfaces from the brownish surfaces of the side surfaces determined bythe height direction and the length direction in FIG. 1. Furthermore, inExamples 1 through 4, it has been successfully confirmed that the firstouter layers 22 a and the second outer layers 22 b are strongly coupledthrough the formation of the boundary reaction layers 24. In addition,Examples 1 through 4 all meet the condition for passing the bendingstrength test, and it has been successfully confirmed that there is noproblem when the multilayer ceramic capacitors according to therespective examples are mounted on boards.

On the other hand, Comparative Example 1 has failed to achieve the outerlayer discrimination, because of using the ceramic raw material powderscomposed of the same main constituent for the first ceramic dielectriclayers and the second ceramic dielectric layers.

In addition, in Comparative Example 2, on the preparation as amultilayer ceramic capacitor, substantially 30% of the boundary surfacewas partially peeled at the boundary between the first outer layer 22 aand the second outer layer 22 b. In addition, while the bending strengthtest was conducted after sorting uncracked samples from the standpointof appearance under a stereoscopic microscope, many samples peeledpartially at the boundary between the first outer layer 22 a and thesecond outer layer 22 b after the test, and the bending strength testwas thus determined to be “x”.

Moreover, in Comparative Example 3, boundary reaction layers were formedbetween the first outer layers 22 a and the second outer layers 22 b, itwas not possible to discriminate between the color of the surfaces ofthe first outer layers and the color of the surface of the inner layerportion (outer layer discrimination).

It is to be noted that the present invention is not to be consideredlimited to the previously described preferred embodiments, but variousmodifications are made within the spirit and scope of the presentinvention. In addition, the thickness and number of ceramic layers,opposed electrode area, and the external dimensions of the multilayerceramic capacitor are not to be considered limited thereto.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A multilayer ceramic capacitor comprising: alaminated body including an inner layer portion including a plurality offirst ceramic dielectric layers laminated and internal electrodesprovided on the plurality of first ceramic dielectric layers; and anouter layer portion including a plurality of second ceramic dielectriclayers laminated outside the inner layer portion, the plurality ofsecond ceramic dielectric layers having no internal electrodes providedthereon; and external electrodes provided on both ends of the laminatedbody; wherein the inner layer portion contains, as a main constituent, aperovskite compound represented by ABO₃, where A represents one or moreof Ba, Sr, and Ca, B represents one or more of Ti, Zr, and Hf, and Orepresents oxygen; the outer layer portion includes at least a firstouter layer containing an oxide as a main constituent, the first outerlayer being an outermost layer, and a second outer layer containing, asa main constituent, an oxide that is different from the oxide of thefirst outer layer; a boundary reaction layer is disposed between thefirst outer layer and the second outer layer; the boundary reactionlayer contains at least one element other than oxygen among elementsconstituting the oxide in the first outer layer adjacent to the boundaryreaction layer, and at least one element other than oxygen amongelements constituting the oxide in the second outer layer adjacent tothe boundary reaction layer; and a surface of the first outer layerdiffers in color from a surface of the inner layer portion.
 2. Themultilayer ceramic capacitor according to claim 1, wherein the oxide inthe second outer layer is a perovskite compound.
 3. The multilayerceramic capacitor according to claim 2, wherein the oxide in the firstouter layer is a perovskite compound.
 4. The multilayer ceramiccapacitor according to claim 1, wherein the laminated body has a cuboidshape.
 5. The multilayer ceramic capacitor according to claim 1, whereinthe plurality of first dielectric layers and the plurality of seconddielectric layers each have a thickness of about 0.5 μm to about 5 μm.6. The multilayer ceramic capacitor according to claim 1, wherein theouter layer portion is a first outer layer portion, and a second outerlayer portion is provided in the laminated body such that the innerlayer portion is located between the first and second outer layerportions.
 7. The multilayer ceramic capacitor according to claim 6,wherein the first outer layer portion has a different thickness thanthat of the second outer layer portion.
 8. The multilayer ceramiccapacitor according to claim 6, wherein the second outer layer portionincludes a third outer layer and a fourth outer layer, and a boundaryreaction layer disposed between the third outer layer and the fourthouter layer.
 9. The multilayer ceramic capacitor according to claim 6,wherein the second outer layer portion does not include a boundaryreaction layer.
 10. The multilayer ceramic capacitor according to claim1, wherein the plurality of first ceramic dielectric layers aredifferent in color from the plurality of second ceramic dielectriclayers.
 11. The multilayer ceramic capacitor according to claim 1,wherein the plurality of first ceramic dielectric layers are white. 12.The multilayer ceramic capacitor according to claim 1, wherein theexternal electrodes extend along both ends in a longer direction of thelaminated body.
 13. The multilayer ceramic capacitor according to claim1, wherein the external electrodes wrap around four side surfaces fromend surfaces of the laminated body.
 14. The multilayer ceramic capacitoraccording to claim 1, wherein the external electrodes include underlyingsintered metal paste layers and plating layers on the underlyingsintered metal paste layers.
 15. A method of determining an orientationof an electronic component, the method comprising the steps of:providing the multilayer ceramic capacitor according to claim 1;determining a difference in color between the surface of the first outerlayer and the surface of the inner layer portion; and determining apositional relationship of the multilayer ceramic capacitor based on aresult of the step of determining the difference in color.
 16. Themethod according to claim 15, further comprising the step of aligningand mounting the multilayer ceramic capacitor on a board or substratebased on a result of the step of determining the orientation of theinternal electrodes.